This invention relates to improved slip assemblies for supporting a well pipe in a rotary table.
Each time that a length of pipe is added to or removed from a drill string, the string must be temporarily supported by slips positioned within a tapered slip bowl structure in a rotary table. After the desired length of pipe has been added or removed, the slips are released to permit vertical movement of the string. On occasions when the entire string must be removed from the well, as for replacement of a bit or for other similar purposes, the necessity for repeated movement of the slips into and out of active position in first successively breaking a large number of connections in the string as it is removed from the well, and then remaking these connections when the string is again lowered into the well, results in the expenditure of a great deal of time and effort just in slip handling. Where the slips are handled entirely manually, their usually very substantial weight renders it rather difficult for the workmen to lift the slips into and out of the bowl, and there is also an ever present danger of injury in such handling of the slips.
In an attempt to overcome these difficulties, various types of power slip arrangements have been proposed in the past, in which a power operated unit has been employed to suspend the slips above the slip bowl, and in some way utilize power for effecting at least a portion of the slip movement. For example, such power slip arrangements have been shown in U.S. Pat. Nos. 2,939,683, 3,210,821, 3,270,389, 3,457,605, 3,961,399, 2,570,039 and 2,641,816. Some of these have been effective in operation, and have seen substantial use, but many drilling companies have continued to use manual slips because of the high cost of power slip units, and because most power slip units require permanent attachment of a support post or other structure to the rig floor at the side of the rotary table. Space is at a premium on the rig floor, and many drillers hesitate to occupy a portion of that space permanently by equipment which during much of the time will not be in use and may interfere with other operations.
U.S. Pat. No. 2,607,098 shows a slip arrangement in which a plurality of slips are supported by a slip bowl structure for relative upward and downward movement, and can be releasably supported in an upper inactive position. U.S. Pat. No. 2,340,597 shows a device in which an actuating mechanism manually operable from a side of the well pipe can move a slip carrier upwardly and downwardly relative to a slip bowl. U.S. Pat. Nos. 2,151,208, 2,245,592 and 3,742,562 show well pipe supporting `spiders`, which include vertically movable slips, but which are not capable of rotating with the pipe as is desirable in a rotary table arangement of the type with which the present invention is concerned. The first of these three patents, U.S. Pat. No. 2,151,208 shows a spider body having slips which are actuable upwardly and downwardly by a pivoting lever, with a spring urging the slips downwardly to their active position and a latch being operable to hold the lever in its retracted condition.